The invention is related to the field of ice adhesion, specifically, to increasing selectively the friction between ice and the surfaces of solid objects, in particular, to surfaces in transportation systems.
Statement of the Problem
Skidding, slipping and sliding on ice surfaces cause numerous types of problems. Ice on roads is frequently a cause of automobile accidents resulting in personal injury and death, as well as material damage. Large amounts of material resources, money and man-hours are spent annually to remove ice and snow from roads and other automotive surfaces and to reduce risks of slipping and skidding on iced surfaces. The accidents and time delays associated with icy roads are major causes of inconvenience and personal and economic damage.
Effects of DC electrical fields on friction between ice and a xe2x80x9csliderxe2x80x9d have been reported in the literature. See, for example, xe2x80x9cThe effect of static electric field on ice frictionxe2x80x9d, V. Petrenko, Journal of Applied Physics, 76 (2), 1994; xe2x80x9cElectromechanical Phenomena in Icexe2x80x9d, V. Petrenko, Special Report 96-2, US Army Corps of Engineers CRREL, 1996. The experiments reported in these publications were restricted to DC electric fields. Also, these publications did not teach practical uses of electric fields to increase friction between a solid surface and ice.
The invention helps to solve some of the problems mentioned above by providing systems and methods for modifying the friction force between ice and the surfaces of solids. Systems and methods in accordance with the invention are particularly applicable to problems associated with ice and surfaces in the field of automotive transportation; however, systems and methods in accordance with the invention are generally applicable to reduce problems caused by skidding, slipping and sliding on ice.
In systems and methods in accordance with the invention, friction between a solid object and a layer of ice is increased by generating a strong electric field at the contact interface of the solid and the ice. A strong electric field at the contact interface is generated in a system including: a plurality of electrodes in the solid object, wherein the electrodes are located proximate to the contact interface; and a power source electrically connected to the electrodes, wherein the power source is capable of providing a potential difference across the electrodes to generate an electric field at the contact interface. The electric field strength at the contact interface typically has a value in a range of from 100 V/cm to 105 V/cm. Preferably, an AC power source provides the potential difference to generate an AC electric field at the contact interface. Typically, the AC electric field has a frequency not exceeding 1000 Hz. Preferably, the AC electric field has a frequency not exceeding 200 Hz. More preferably, the AC frequency is in a range of about 5 to 100 Hz. An advantage of a system and a method in accordance with the invention is that relatively low-frequency power may be used to generate an AC electric field at the contact interface. Alternatively, the power source may be a DC power source.
In embodiments in accordance with the invention, the interelectrode spacing separating oppositely polarized electrodes is preferably as small as possible. Generally, the electrodes are separated from each other by an interelectrode spacing not exceeding 10 mm. Preferably, the interelectrode spacing does not exceed 100 micrometers (xcexcm). The electrodes may be interdigitated. Also, the electrodes should be at or as close as possible to the contact interface of the surfaces of the solid object and the ice. In this specification, the term xe2x80x9cproximate to the contact interfacexe2x80x9d means at the contact interface or within 1 cm of the contact interface. The region between electrodes corresponding to the interelectrode spacing contains electrically insulating material so that the voltage difference across the electrodes generates a strong electric field. Thus, the solid object typically comprises electrical insulation that insulates each of the electrodes. Each electrode preferably possesses an electrical conductivity greater than 10xe2x88x9210 Siemens/cm (xe2x80x9cS/cmxe2x80x9d). The solid object may contain dopants to increase electrical conductivity in the electrodes. A common application of the invention is to increase friction between a layer of ice covering a paved surface and a rubber tire of an automobile or airplane. Electrodes in the rubber tire may be fabricated by including dopants in regions of the tire near its cylindrical outer surface to make conductive electrode regions. For example, the rubber tire may contain carbon black to impart or increase electrical conductivity.
Embodiments in accordance with the invention are useful in a wide variety of situations. For example, the solid object may be, among others, a rubber tire, a wheel of a rail vehicle, a track of a tracked vehicle, a shoe sole, or a snow ski. A system in accordance with the invention may comprise a plurality of conductive solid objects, each solid object forming a contact interface with ice, and each solid object including a plurality of electrodes. In such cases, a power source is electrically connected to each of the electrodes. The supplied electrical power provides a potential difference across each pair of adjacent electrodes. The potential difference generates an electric field at the ice-solid contact interfaces. For example, the invention may be utilized in two or more tires of an automobile.
The power source provides a voltage in a range of about 1 to 5000 volts, but more commonly in a range of about 5 to 2000 volts. Preferably, a power source providing a voltage not exceeding 500 volts generates a sufficiently strong electric field at the contact interface to increase friction. Under preferred conditions, when the interelectrode spacing is less than one mm, and the electrodes are located within one mm of the contact interface, a voltage in a range of about 5 to 100 volts is effective.
In preferred embodiments, only a small group of electrode pairs, which are proximate to the ice-solid contact interface, are electrically connected to the power source, while electrodes that are not proximate to the contact interface are not electrically connected to the AC power source. Various types of switching mechanisms are useful for connecting and disconnecting the AC power source to electrodes. In tires, for example, the electrical connection may be achieved with slip rings that are similar to the slip rings used in electromotors. (In electromotors, the slip rings provide connections of the rotor coils that are directly opposed to the static electromagnets.) Another feature in preferred embodiments is an additional impedance between the AC power source and the electrodes to limit AC current at the electrodes. Typically, a capacitor is located in series between the AC power source and the electrodes.
The invention is next described further in connection with preferred embodiments, and it will become apparent that various additions, subtractions, and modifications can be made by those skilled in the art without departing from the scope of the invention.